1. Field of the Invention
The invention relates to a sign adapted to be backlit such as it is used, for example, as an indicating light in buildings and vehicles and particularly in airplanes.
2. Description of Related Art
In a plurality of applications, information is visually indicated via display surfaces adapted to be backlit (U.S. Pat. No. 5,263,271, U.S. Pat. No. 2001/053071, European Patent No. 0 547 943, Japanese Patent No. 09 311 650, DE-C-40 06 649). Such signs adapted to be backlit can be found, for example, in airplanes to indicate whether the toilets are occupied or not or to illustrate the “fasten your seatbelt” and “no smoking” signs. The two last-mentioned visual signs are located directly above the passengers and form part of the so-called passenger service units (PSU).
Basically, backlit sign surfaces consist of a transparent plastic material as cover element on the front side of which indication information is printed for illustrating the symbols or the like. Over this printed front side, an opaque lacquer is applied which is laid bare in the region of the symbols. Subsequently, the entire front side of the cover element is then coated with a translucent color. Due to this color layer application, the symbol fields shall hardly be detectable and ideally be non-detectable for the observer when they are not backlit.
In practice, however it has turned out that the front side of the cover elements structured due to the application of the diverse lacquer layers is nevertheless relatively clearly visible because of shadow effects of the ambient light when the symbol fields are not backlit. This is found not very aesthetically appealing.
In prior art, it is further known to use printed sheets at the front side of the front cover of operating units, these sheets being injection-molded from behind with plastics. The sheets are printed with an opaque color and only transparent in the region of the symbol zone to be backlit. These symbol zones shall also be visually detectable without backlighting, e.g., in daylight.
Accordingly, there is an ongoing need to improve the visual appearance of a sign adapted to be backlit, particularly when the sign is not backlit.